It鈥檚 been a mystery since before the time that Charles Darwin observed spiders launching from the HMS Beagle with 鈥渦naccountable rapidity鈥�, carried aloft by silken threads. It now seems that spiders fly using the force of atmospheric electricity.
Many spiders are excellent fliers, despite not having wings. They 鈥渂alloon鈥� through the air using silk fibres which act like a paraglider, travelling hundreds of miles and reaching heights of 4.5 kilometres. It was assumed that they took to the air on the breeze, but Erica Morley at the University of Bristol wanted to test an idea proposed nearly 200 years ago: that electrostatic forces 鈥� the way objects are attracted or repulsed because of their charge 鈥撀� could be enough to get spiders airborne.
First, Morley and colleagues tested whether spiders could sense electrical fields. They put small Linyphiid spiders in a Faraday cage that shielded them from electromagnetic fields and air currents, then added their own electrical fields that mimicked the forces seen in nature. 鈥淲e were looking for changes in behaviour in response to switching on and off the electric field,鈥� says Morley.
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Electric boogaloo
When the current was switched on, the spiders started a behaviour known at tiptoeing which is only seen when spiders are about to balloon 鈥� straightening their legs, raising their abdomen and releasing silk. The researchers also found that the spiders had minute sensory hairs that can detect electric fields. 鈥淭hey can feel the charge in the air,鈥� says Morley. This is the first time this sensory ability has been documented in creatures other than bees.
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The second part of the experiment examined the effect of the electric field on airborne spiders, and found that the height of the spiders could be controlled by raising or lowering the electrical field. 鈥淚f you switch the voltage off, you see the spiders slowly start to drop. You can play with their altitude,鈥� says Morley.
Other researchers are impressed that this long-standing conundrum has been solved. 鈥淚t is very satisfying to see this proved in such a convincing way,鈥� says physicist Peter Gorham of the University of Hawaii, whose theoretical calculations of the inspired Morley鈥檚 study.
It is theoretically possible that tiny, light-weight drones could one day take to the air in the same way as ballooning spiders, he speculates. 鈥淪piders weighing 100mg can balloon. That鈥檚 more than enough to fly a tiny microprocessor and camera.鈥�
